Generally, in an uplink transmission, a mobile station (hereinafter “MS”) use the radio resources allocated by the base station (hereinafter “BS”) as designated. This system can be called as a single-user system. For example, in the Time Division Multiple access (TDMA) system, certain time interval is allocated to each of the MSs, and the allocated time interval can be used by the allocated MS as designated. On the other hand, in the Code Division Multiple Access (CDMA) system, different codes are allocated to each of the MSs, and each of the MSs use the allocated code as designated. In this case, one code that can be called as one radio resource can be used only one user.
FIG. 1 is an illustrative figure that shows an example of the radio resource allocated to MSs in multi-carrier system. As shown in the FIG. 1, in the multi-carrier system, radio resources in the map consisting of a time axis and a frequency axis can be allocated to each of the MSs, and each of the MSs can use the allocated radio resource as designated.
FIG. 2 is an illustrative figure that shows another example of the radio resource allocated to MSs in multi-carrier system. As shown in the FIG. 2, the same radio resource in the map consisting of a time axis and a frequency axis can be allocated to and shared by 2 or more MSs, and this system is called as multi-user system.
Table 1 is an example that represents a method for transmitting signals by each of the MSs in the multi-user system.
TABLE 1MS 1S1MS 2S2
As in the table 1, when each of the MSs transmits signals as in the single user-system, and base station receives two signals at once, the data rate becomes doubled, and theoretical transmission rate also becomes doubled. But, there is a problem of increasing error rate in the receiving side.
Table 2 is another example that represents a method for transmitting signals by each of the MSs in the multi-user system.
TABLE 2MS 1S1S1MS 2S2−S2
When transmitting as in the table 2, each of the MSs repeats same signal twice and transmits on the time axis or on the frequency axis. Instead of sharing the same radio resource, each of the MSs transmits the same signal repeated twice, so the data rate becomes 1 as in the single-user system. Here, the signals of the two MSs, that is repeated twice, is configured to have an orthogonality to each other, so they don't give interference to each other MS. According to this transmission method, although the data rate is reduced in half for transmitting the signal repeated twice, it can make up for the low performance in the low Signal to Noise Ratio (SNR) environment. Moreover, because orthogonality can be maintained for each of the data, the signals can be easily decoupled.
In the prior multi-user multi-input multi-output system, orthogonality can be obtained by the method as in the table 2, but there is a problem that it can't obtain the diversity gain because transmitting signals repeated on the neighboring time axis or frequency axis.